Methods of forming capacitors

ABSTRACT

A method of forming a capacitor includes forming a conductive metal first electrode layer over a substrate, with the conductive metal being oxidizable to a higher degree at and above an oxidation temperature as compared to any degree of oxidation below the oxidation temperature. At least one oxygen containing vapor precursor is fed to the conductive metal first electrode layer below the oxidation temperature under conditions effective to form a first portion oxide material of a capacitor dielectric region over the conductive metal first electrode layer. At least one vapor precursor is fed over the first portion at a temperature above the oxidation temperature effective to form a second portion oxide material of the capacitor dielectric region over the first portion. The oxide material of the first portion and the oxide material of the second portion are common in chemical composition. A conductive second electrode layer is formed over the second portion oxide material of the capacitor dielectric region.

TECHNICAL FIELD

The invention is related to methods of forming capacitors.

BACKGROUND OF THE INVENTION

A continuing goal in integrated circuitry fabrication is to form thecircuitry components to be smaller and denser over a given area of asemiconductor substrate. One common circuit device is a capacitor, whichhas a capacitor dielectric region received between a pair of conductiveelectrodes. In such devices, there is a continuous challenge to maintainsufficiently high storage capacitance despite decreasing area in thedenser circuits. Additionally, there is a continuing goal to furtherdecrease cell area. One manner of increasing cell capacitance is throughcell structure techniques. Such techniques include three-dimensionalcell capacitors, such as trench or stacked capacitors.

Highly integrated memory devices, for example 256 Mbit DRAMs and beyond,are expected to require a very thin dielectric film for thethree-dimensional capacitors of cylindrically stacked, trenched or otherstructures. To meet this requirement, the capacitor dielectric filmthickness will be below 2.5 nanometer of SiO₂ equivalent thickness.Accordingly, materials other than SiO₂ having higher dielectricconstants are expected to be used. Si₃N₄ is one such material which hasbeen used either alone or in combination with silicon dioxide as acapacitor dielectric region. Insulating inorganic metal oxide materials,for example Al₂O₃, Ta₂O₅ and barium strontium titanate, have even higherdielectric constants and low leakage currents which make them attractiveas capacitor dielectric materials for high density DRAMs, non-volatilememories and other integrated circuitry.

In many of such applications, it will be highly desirable to utilizemetal for the capacitor electrodes, thus forming a metal-insulator-metal(MIM) capacitor. In the context of this document, a “metal” encompasseselemental metals, alloys of elemental metals, and metal compoundsregardless of stoichiometry. Exemplary conductive metals proposed foruse with Al₂O₃ as the capacitor dielectric material include titaniumnitride, tungsten nitride and tantalum nitride. Unfortunately, thesematerials can be appreciably oxidized when exposed to the typicalchemical vapor deposition or atomic layer deposition (ALD) techniquesunder which Al₂O₃ (or other dielectric materials) would be deposited.The oxides which form typically have a reduced dielectric constant orincreased leakage than Al₂O₃, thereby having an adverse effect on thecapacitor being fabricated. It would be desirable to at least reduce thedegree of oxidation of a metal capacitor electrode layer during theformation of an oxide dielectric thereover.

While the invention was motivated from this perspective, it is in no wayso limited. The invention is only limited by the accompanying claims,appropriately interpreted in accordance with the doctrine ofequivalents, without limiting reference to the specification, and withthe specification herein only providing but exemplary preferredembodiments.

SUMMARY OF THE INVENTION

The invention includes methods of forming capacitors. In oneimplementation, a method of forming a capacitor includes forming aconductive metal first electrode layer over a substrate, with theconductive metal being oxidizable to a higher degree at and above anoxidation temperature as compared to any degree of oxidation below theoxidation temperature. At least one oxygen containing vapor precursor isfed to the conductive metal first electrode layer below the oxidationtemperature under conditions effective to form a first portion oxidematerial of a capacitor dielectric region over the conductive metalfirst electrode layer. At least one vapor precursor is fed over thefirst portion at a temperature above the oxidation temperature effectiveto form a second portion oxide material of the capacitor dielectricregion over the first portion. The oxide material of the first portionand the oxide material of the second portion are common in chemicalcomposition. However, the oxide of the second material might be ofhigher density and have superior electrical properties as compared tothe first portion of the oxide material. A conductive second electrodelayer is formed over the second portion oxide material of the capacitordielectric region.

In one implementation, a method of forming a capacitor includes forminga conductive metal first electrode layer over a substrate, with theconductive metal first electrode layer being oxidizable to a higherdegree at and above an oxidation temperature as compared to any degreeof oxidation below the oxidation temperature. A capacitor dielectricregion is formed over the conductive metal first electrode layer byatomic layer deposition. The atomic layer deposition comprises forming afirst portion of the capacitor dielectric region at a temperature belowthe oxidation temperature, and forming a second portion of the capacitordielectric region over the first portion at a temperature above theoxidation temperature. The first portion restricts oxidation of theconductive metal first electrode layer during formation of the secondportion. A conductive second electrode layer is formed over the secondportion of the capacitor dielectric region.

Other aspects and implementations are contemplated.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic sectional view of a semiconductor waferfragment in process in accordance with an aspect of the invention.

FIG. 2 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown by FIG. 1.

FIG. 3 is a view of the FIG. 2 wafer fragment at a processing stepsubsequent to that shown by FIG. 2.

FIG. 4 is a view of the FIG. 3 wafer fragment at a processing stepsubsequent to that shown by FIG. 3.

FIG. 5 is a diagrammatic sectional view of a semiconductor waferfragment in process in accordance with an aspect of the invention.

FIG. 6 is a view of the FIG. 5 wafer fragment at a processing stepsubsequent to that shown by FIG. 5.

FIG. 7 is a view of the FIG. 6 wafer fragment at a processing stepsubsequent to that shown by FIG. 6.

FIG. 8 is a view of the FIG. 7 wafer fragment at a processing stepsubsequent to that shown by FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

The invention is described in a first preferred embodiment in connectionwith FIGS. 1-4. FIG. 1 depicts a semiconductor substrate 10 comprisingbulk monocrystalline silicon material 12. In the context of thisdocument, the term “semiconductor substrate” or “semiconductivesubstrate” is defined to mean any construction comprising semiconductivematerial, including, but not limited to, bulk semiconductive materialssuch as a semiconductive wafer (either alone or in assemblies comprisingother materials thereon), and semiconductive material layers (eitheralone or in assemblies comprising other materials). The term “substrate”refers to any supporting structure, including, but not limited to, thesemiconductive substrates described above. Further in the context ofthis document, the term “layer” encompasses both the singular and theplural, unless otherwise indicated.

An insulative layer 14, for example silicon dioxide, is formed oversubstrate material 12. By way of example only, such depicts a substrateover which a capacitor will be fabricated. Any conceivable substrate iscontemplated, whether existing or yet-to-be developed. A conductivemetal first electrode layer 16 is formed over substrate 12/14. Suchmaterial is oxidizable at and above some oxidation temperature in thepresence of an oxygen containing material to a higher degree at andabove such temperature as compared to any degree of oxidation below suchtemperature. The oxidation temperature referred to is not necessarilythe minimum temperature at which the material will oxidize in thepresence of the oxygen containing material, for example as conditions inaddition to temperature can effect whether a given material willoxidize. Rather, the stated oxidation temperature can be any temperatureat which the material can oxidize in the presence of the oxygencontaining material. Exemplary conductive metals include metal nitridessuch as titanium nitride, tungsten nitride and tantalum nitride. Thesematerials appreciably oxidize in the presence of many oxygen containingmaterials at an exemplary oxidation temperature of 300° C. and above.Electrode layer 16 might be formed by any existing or yet-to-bedeveloped method, for example by sputtering, chemical vapor depositionand/or atomic layer deposition.

Referring to FIG. 2, at least one oxygen containing vapor precursor isfed to conductive first metal electrode layer 16 below the selectedoxidation temperature under conditions effective to form a first portionoxide material 18 over conductive metal first electrode layer 16.Accordingly with the above exemplary materials, an exemplary preferredoxidation temperature below which the at least one vapor precursor isflowed is 300° C., by way of example only 290° C. First portion 18 willcomprise a portion of a capacitor dielectric region 20, as will beapparent from the continuing discussion. By way of example only, anexemplary preferred material is aluminum oxide. Also as shown, firstportion 18 is preferably formed “on” (meaning in direct physical contactwith) conductive metal first electrode layer 16. Most preferably, firstportion oxide material 18 is formed without any measurable oxidationoccurring of metal first electrode layer 16, although some oxidationthereof is not precluded in the broadest considered aspects of theinvention, as claimed. By way of example only, the conditions mightinclude chemical vapor deposition (for example feeding multiple vaporprecursors simultaneously to the substrate), atomic layer deposition,yet-to-be developed methods and/or any combination thereof. For examplewith respect to atomic layer deposition, the conditions might includeprevious formation of a monolayer to which one or more multiple oxygencontaining precursor feeds occur.

Referring to FIG. 3, at least one vapor precursor is fed over firstportion 18 at a temperature above the oxidation temperature effective toform a second portion oxide material 22 of capacitor dielectric region20 over first portion 18. In one preferred embodiment, the precursorflowing during the formation of the second portion oxide material is ata temperature which is at least 25° C. higher than during the formationof the first portion oxide material, in another preferred embodiment ata temperature which is at least 50° C. higher, and in yet anotherpreferred embodiment at a temperature which is at least 100° C. higher.Regardless, the oxide material of first portion 18 and second portion 22are of the same/common chemical composition. However, the oxide of thesecond material might be of higher density and have superior electricalproperties as compared to the first portion of the oxide material. Thevapor precursor(s) used to form portion 22 might be the same ordifferent from that/those used to form portion 18. Preferably and asshown, second portion 22 is formed on first portion 18. Preferably,second portion 22 is formed using the same general technique by whichfirst portion 18 was formed, for example both by atomic layer depositionor both by chemical vapor deposition. Further preferably, first portion18 and second portion 22 are formed in the same/common depositionchamber without removing the substrate from such chamber intermediatethe formation of the first and second portions. In one preferredimplementation, the second portion oxide material and the first portionoxide material are formed using at least the same pressure and same oneor more precursors. In one preferred implementation, the second portionoxide material is formed using identical conditions (meaning at leastthe same pressure, precursors and flow rates) under which the firstportion oxide material is formed, but for different temperature. Mostpreferably, first portion 18 restricts oxidation of the conductive metalfirst electrode layer during the formation of second portion 22. Forexample with respect aluminum oxide, the initial deposition of portion18 at the lower temperature forms a less dense aluminum oxide than thealuminum oxide of portion 22 formed at the higher temperature, withportion 18 restricting oxidation of the underlying metal duringformation of portion 22.

First and second portions 18, 22 might be formed to the same respectivethickness, or to different thicknesses. Typically, and for example withrespect to aluminum oxide, deposition of first portion 18 attemperatures below which significant oxidation would occur under typicaldeposition conditions and times results in a less than desired densitylayer (at least as initially deposited). Accordingly in one preferredembodiment, first portion 18 is formed to a thickness which is less thanthat of second portion 22, more preferably to a thickness which is nogreater than one-third that of the second portion, and even morepreferably to a thickness which is no greater than one-fifth that of thesecond portion.

Referring to FIG. 4, a conductive second electrode layer 24 has beenformed over second portion oxide material 22, and preferably on suchmaterial as shown, of capacitor dielectric region 20. Preferredmaterials include conductive metal materials, for example the conductivemetal nitrides referred to above. In one exemplary preferred embodiment,the entirety of the capacitor dielectric region 20 intermediate firstelectrode layer 14 and second electrode layer 24 consists essentially ofaluminum oxide. Exemplary preferred thickness ranges for each ofelectrodes 16 and 24 include from 100 Angstroms to 200 Angstroms, withan exemplary thickness range for capacitor dielectric region 20 beingfrom 40 Angstroms to 60 Angstroms.

By way of example only, exemplary capacitor dielectric materials includeany one or combination of HfO₂, Ta₂O₅, Y₂O₃, ZrO₂, HfSiO₄, ZrSiO₄ andYSiO₄. Further, non-oxygen containing capacitor dielectric materialsmight be employed alternately or in addition to oxygen containingcapacitor dielectric materials. Where an oxide is to be formed,exemplary oxidizers include O₂, O₃, H₂O, NO₂, NO and any alcohols(including polyols). Exemplary precursors include metallorganicprecursors, for example tertbutylaluminum alkoxide, triethylaluminum,trimethylaluminum, tetrakisdimethylamido hafnium, pentathoxy tantalum,n-butyl cyclopentadienyl yttrium, and other metal alkyls or metalalkoxides.

While the above described embodiment shows the layers as being blanketlydeposited, any partial deposition technique (whether existing oryet-to-be developed) is also of course contemplated. Further, therespective illustrated layers can patterned at any time into a desiredshape of a capacitor if not deposited or otherwise initially formed insuch shape.

By way of example only, an exemplary method of forming a capacitor usingatomic layer deposition at least in part for the formation of acapacitor dielectric layer is described with reference to FIGS. 5-8 withrespect to a substrate 10 a. Like numerals from the first describedembodiment have been utilized where appropriate, with differences beingindicated with the suffix “a” or with different numerals. Referring toFIG. 5, a conductive metal first electrode layer 16 has been formed overa substrate, with the conductive metal being oxidizable to a higherdegree at and above an oxidation temperature as compared to any degreeof oxidation below the oxidation temperature. Exemplary preferredmaterials are as described above with respect to the FIGS. 1-4embodiment. A metal containing first species is chemisorbed to form afirst species monolayer 30 from a gaseous first precursor ontoconductive metal first electrode layer 16. In the illustrated example,an exemplary gaseous first precursor is trimethylaluminum forming ametal containing first species in the form of Al(CH₃)_(x).

Referring to FIG. 6, at a temperature below the selected oxidationtemperature of at least the outermost portion of material 16, thechemisorbed first species has been contacted with an oxygen containinggaseous second precursor to react with the first species and form adielectric oxide monolayer 35 which comprises the metal of the firstspecies, namely the aluminum as shown in the illustrated example.Exemplary oxygen containing gaseous second precursors are any of thoseoxidizers identified above. Of course, monolayers 30 and 35 as describedabove might be discontinuously formed with respect to their respectiveunderlying substrates. Such discontinuous or less than saturatedmonolayers are, however, considered a monolayer in the context of thisdocument. Further, multiple of the above-described chemisorbings andcontactings might be repeated once or multiple times prior to furtherprocessing. Further, the above-described chemisorbing and contactingmight be conducted at a common temperature or at different temperatures,and even under other different conditions. Further, inert gas flow mightbe included with or intermediate the respective chemisorbing andcontacting, or the deposition chamber pumped down without any inert gasfeed towards purging the respective gaseous precursors from the chamber.

Referring to FIG. 7, the metal containing first species is chemisorbedfrom the gaseous first precursor to form another first species monolayer40 over the substrate which comprises the dielectric metal oxide.

Referring to FIG. 8, at a temperature above the oxidation temperature,the another first species monolayer 40 is contacted with an oxygencontaining gaseous second precursor (i.e., the same or different asutilized above) to react with the first species and form anotherdielectric metal oxide monolayer 45 comprising the metal of the firstspecies. During such formation, dielectric metal oxide monolayer 35comprises a shield which, at least partially, restricts oxidation ofconductive metal electrode layer 16 during such contacting of theanother first species monolayer with the oxygen containing gaseoussecond precursor. As above, said monolayer 45 might be discontinuouslyformed/less than saturated such that the FIGS. 7 and 8 chemisorbing andcontacting might be repeated at least once or multiple times more, priorto subsequent processing. Further as alluded to above, it might bedesirable that the thickness of the sub-oxidation temperature materialbe greater than a saturated monolayer thick and, as well, be less than atotal thickness of a second portion of the metal oxide layer beingformed. Accordingly, the exemplary depicted chemisorbings andcontactings exemplified by FIGS. 7 and 8 might be repeated more timesthan are the chemisorbings and contactings depicted by FIGS. 5 and 6,for example at least five times more, to achieve a corresponding thickersecond portion as compared to the first portion. Also, the chemisorbingand contacting exemplified by the FIGS. 7 and 8 processings might beconducted at a common temperature or different temperatures.

A conductive second electrode layer would be formed over, and preferablyon, the another dielectric metal oxide monolayer, typically as describedabove with respect with the first described embodiment.

By way of example only, for a material which has an oxidationtemperature of around 300° C., the processing depicted by FIG. 6 wouldbe conducted at a temperature no greater than 300° C., and theprocessing depicted by FIG. 8 would be conducted at a temperature of atleast 325° C., and could of course be conducted at a higher temperature,for example of at least 425° C.

An exemplary preferred deposition range for the first portion formedwith present generation processing is from about 5 Angstroms to about 20Angstroms, with an exemplary thickness for the second portion being fromabout 10 Angstroms to about 40 Angstroms. An exemplary prior art atomiclayer deposition method of forming an Al₂O₃ layer includes an aluminumprecursor of trimethyl aluminum and an oxygen containing precursor of anO₃ and O₂ mixture containing from 5% to 20% by weight O₃. Prior artdepositions have occurred at temperatures above 300° C., with 460° C.being a specific example. Pressure typically ranges from 200 mTorr to 5Torr, with 1 Torr being a specific example. The typical thickness of thealuminum oxide formed for the capacitor dielectric layer is about 50Angstroms, with metal electrode material therebeneath formingundesirable quantities of oxides of the metal of the underlyingelectrode material.

In a reduction-to-practice example in accordance with an aspect of theinvention, a first portion of the oxide material, as described above,was formed in six complete ALD cycles using the above precursors at 250°C. and a pressure of 1 Torr. The substrate was received within a chamberhaving a volume of from about 1 liter to 2 liters, and the precursorpulses lasted from 1 to 2 seconds, respectively, with intervening inertargon purge pulsings. Such resulted in an average thickness of a firstportion as described above which was substantially continuous/saturatedat about from 4 Angstroms to 5 Angstroms, resulting in a probablydiscontinuous average deposition thickness of about 0.8 Angstroms percycle. This was followed under otherwise identical conditions but at anincreased temperature of 450° C. for about 50 complete depositioncycles, which resulted in a 40 Angstrom thick second portion at thehigher deposition temperature, and without noticeable oxidation of theunderlying metal nitride electrode material.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means whereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A method of forming a capacitor, comprising: forming a conductivemetal nitride comprising first electrode layer over a substrate, theconductive metal nitride being oxidizable to a higher degree at andabove an oxidation temperature of 300° C. as compared to any degree ofoxidation below the oxidation temperature of 300° C.; feeding at leastone oxygen containing vapor precursor to the conductive metal nitridecomprising first electrode layer below the 300° C. oxidation temperatureunder conditions effective to form a first portion oxide materialcomprising aluminum oxide of a first density of a capacitor dielectricregion over the conductive metal nitride comprising first electrodelayer; feeding at least one oxygen containing vapor precursor over thefirst portion at a temperature above the 300° C. oxidation temperatureeffective to form a second portion oxide material comprising aluminumoxide of a second density of the capacitor dielectric region over thefirst portion, the oxide comprising material of the first portion andthe oxide material of the second portion being common in chemicalcomposition and the second density being greater than the first density;and forming a conductive second electrode layer over the second portionoxide material of the capacitor dielectric region.
 2. The method ofclaim 1 wherein the first and second portions are formed from a commonvapor precursor.
 3. The method of claim 1 wherein the first and secondportions are formed from different precursors.
 4. The method of claim 1wherein the first and second portions are formed by chemical vapordeposition.
 5. The method of claim 1 wherein the first and secondportions are formed by chemical vapor deposition using at least onecommon vapor precursor.
 6. The method of claim 1 wherein the first andsecond portions are formed by chemical vapor deposition respectivelycomprising feeding multiple vapor precursors simultaneously to thesubstrate.
 7. The method of claim 1 wherein the first and secondportions are formed by chemical vapor deposition respectively comprisingfeeding common multiple vapor precursors simultaneously to thesubstrate.
 8. The method of claim 1 wherein the first and secondportions are formed by atomic layer deposition.
 9. The method of claim 1wherein the first portion is formed on the conductive metal nitridecomprising first electrode layer.
 10. The method of claim 1 wherein thesecond portion is formed on the first portion.
 11. The method of claim 1wherein the first portion is formed on the conductive metal nitridecomprising first electrode layer, and the second portion is formed onthe first portion.
 12. The method of claim 1 wherein the first portionis formed to a thickness which is less than that of the second portion.13. The method of claim 1 wherein the first portion is formed to athickness which is no greater than one-third that of the second portion.14. The method of claim 1 wherein the first portion is formed to athickness which is no greater than one-fifth that of the second portion.15. The method of claim 1 wherein the oxide material consistsessentially of aluminum oxide, and an entirety of the capacitordielectric region intermediate the first and second electrode layersconsists essentially of aluminum oxide.
 16. The method of claim 1wherein the first portion oxide material is formed without anymeasurable oxidation occurring of the metal nitride comprising firstelectrode layer.
 17. The method of claim 1 wherein the second portionoxide material and the first portion oxide material are formed using thesame pressure and same one or more precursors.
 18. The method of claim 1wherein the second portion oxide material is formed using identicalconditions under which the first portion oxide material is formed butfor different temperature.
 19. The method of claim 1 wherein the firstand second portions are formed in a common deposition chamber withoutremoving the substrate from such chamber intermediate formation of thefirst and second portions.
 20. The method of claim 1 wherein theprecursor flowing during formation of the second portion oxide materialis at a temperature which is at least 25° C. higher than duringformation of the first portion oxide material.
 21. The method of claim 1wherein the precursor flowing during formation of the second portionoxide material is at a temperature which is at least 50° C. higher thanduring formation of the first portion oxide material.
 22. The method ofclaim 1 wherein the precursor flowing during formation of the secondportion oxide material is at a temperature which is at least 100° C.higher than during formation of the first portion oxide material. 23.The method of claim 1 wherein the first portion oxide material is formedat a temperature of about 290° C.
 24. The method of claim 1 wherein thecapacitor dielectric region is from 40 Angstroms to 60 Angstroms inthickness.
 25. The method of claim 1 wherein formation of the first andsecond portions is blanketly over the substrate.
 26. The method of claim1 wherein formation of the first and second portions is only partiallyover the substrate.
 27. The method of claim 1 wherein the oxygencontaining vapor precursor in formation of at least one of the first andsecond oxide portions comprises at least one of O₂, O₃, H₂O, NO₂, NO andan alcohol.
 28. The method of claim 27 wherein the oxygen containingvapor precursor in formation of at least one of the first and secondoxide portions comprises an alcohol.
 29. The method of claim 28 whereinthe alcohol comprises a polyol.
 30. The method of claim 1 wherein thefirst portion is formed by chemical vapor deposition and the secondportion is formed by atomic layer deposition.
 31. The method of claim 1wherein the second portion is formed by chemical vapor deposition andthe first portion is formed by atomic layer deposition.